I am a 30yr old male, and I have a 10km (20km round trip) commute to work.
- About 60/40 bike lane/road, and its a city = so can be stop-starty with traffic lights in rush hour.

I was only riding about 3 times a week, and then using my motorbike for the other days.
I have a racer bike, single speed but this is fine as route is nearly all flat.
I was never really pushing it - just cruising = would take around 35-40min to get to work (pending traffic lights)

I am 6ft2 and weigh 210lbs, and therefore BMI says im overweight, so I want to get closer to 180lbs.
Therefore I aim to change my lifestyle to meet this goal.
- I already have a plan with a diet - using DailyBurn to help with this.

I imagine I will end up doing some running at some point and also keeping an eye on ebay for some weights.
- However, I am a busy person. Ideally I prefer the idea of maximising my use of time and turn my commute into a more efficient method of losing weight (and as a bonus getting to work quicker, saving more time).

I think I already know the answer - Cycle Harder
I would prefer more detailed answers with advice on motivating me to do this.
- I was thinking perhaps a speedo for my bike to keep track on times/average speeds/etc, but the traffic lights surely make this tricky to rely on?

Any tips (with weight loss in mind) would be great.

I was thinking about putting this in the bicycle-se, but I think its more fitness related.

I also read this post which is related but not a duplicate.
This post on how to make your commute productive is not really related, but I also aim to take advice from there too.

@Ryan, perhaps you can show him a simple calculation that the difference between just cyling for 30-60 mins vs reducing his calorie uptake. Showing that the latter is far more effective, thus that the physical activity should be done for a general health benefit but not (just) losing weight)
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Ivo Flipse♦Jul 18 '11 at 7:54

You should be extremely skeptical about such estimates, since the effort to go 20 km/h into a 10 km/h headwind is nearly ten times as much as going 20 km/h with a 10 km/h tailwind. In addition to wind resistance, hills make a ton of difference. It's nearly 0 effort to go down a steep hill and quite a bit of effort to go up it, and you can easily notice a significant difference in effort with slopes you wouldn't even notice as sloping when walking or driving a car. And acceleration is more effort than cruising at a set speed.

The rolling resistance of a bicycle is quite low and doesn't really change as you go faster. The air resistance for going a given distance increases by the square of your speed. So, yes, if you go the same distance and do it faster, you should burn more calories doing it.

Note though that the difference in the calorie burn between that 16 km/h and 19 km/h speed for two hours (380 kCals) is roughly one bagel with a single pat of butter. There's a lot to be said for adjusting your nutrition to reduce your calorie intake, like Ryan and Ivo suggest in the comments.

A bike computer that measures your speed wouldn't hurt; it would give you something to try to increase. One that measures your cadence (pedaling speed) as well as ground-speed would be better. Best would be a heart rate monitor (which some bike computers support talking to) since that's the most practical way to tell how many calories you're burning. (bike computers that actually measure your power output are prohibitively expensive, however).

For calorie burning, it's usually recommended to do intervals. Basically, after you've warmed up: pedal as hard and fast as you can until your legs burn (30-45 seconds), take it easy for a couple minutes, then push hard again. Making a point of sprinting from the stops is a good way to get some of that kind of push in. This will get your heart rate up and generally burn more calories, but will also help increase your leg strength so that you can do better burning more calories as you progress.

As an avid cyclist, I find it hard to figure out how I would do intervals on a singlespeed. When I want to push myself to go faster, I spin up a bit faster, then shift into a higher gear so that I'm still pushing against a decent amount of resistance. Without shifting I'd just spin out and be unable to push myself harder. Rolling hills on a singlespeed would be very similar to intervals, but it sounds like you don't really have those on your route.

One problem with your (otherwise fine) table is that it is calculated per hour and not per trip. Simon could think "you know what, I will commute with 23km/h instead of 16 km/h and I have doubled my calorie burn". While that is true, he will also be at work within 25 minutes instead of 40, so his total calorie burn is not that much improved as what you would expect (315 vs. 250 kcal).
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AutomatedChaosMay 16 '14 at 6:11